Use of geosynthetic clay liners for pollutant control

The osmotic, hydraulic and self-healing efficiency of bentonite based barriers (e.g. geosynthetic clay liners) for containment of polluting solutes are governed both by the chemico-physical intrinsic parameters of the bentonite, i.e. the solid density, the total specific surface,, and the total fixed negative electric surface charge, and by the chemico-mechanical state parameters able to quantify the solid skeleton density and fabric, i.e. the total and nano void ratio, the average number of platelets per tactoid, the effective electric fixed-charge concentration, and the Stern fraction (fStern). In turn, looking at saturated active clays only, the state parameters seem to be controlled by the effective stress history (SH), ionic valence (νi) and related exposure sequence of salt concentrations in the pore solution (cs). A theoretical framework, able to describe chemical, hydraulic and mechanical behaviours of bentonites in the case of one-dimensional strain and flow fields, has been set up. In particular, the relationships, linking the aforementioned state and intrinsic parameters of a given bentonite with its hydraulic conductivity, effective diffusion coefficient, osmotic coefficient and swelling pressure under different stress-histories and solute concentration sequences, are presented. The proposed theoretical hydro-chemico-mechanical framework has been validated by comparison of its predictions with some of the available experimental results on bentonites (i.e. hydraulic conductivity tests, swelling pressure tests and osmotic efficiency tests).